Spring structural resin molded product, and method and device for forming surface layer on the spring structure resin molded product

ABSTRACT

The present invention relates to a resin-molded article with a spring structure, and to a method and apparatus for preparing a superficial layer of such a resin-molded article with a spring structure which has surfaces free from undulations, comprises fused filaments whose fusion is resistant to separation, maintains its cushioning activity and strength even after long use. A water flows from a cooling water outlet  53   b  into a space between a water-permeating sheet  55  and an inclined plate  51   a . Some part of the flowing water C penetrates the water-permeating sheet  55  to appear on its top surface to form there an overlying current M on which receives lengthwise arranged peripheral continuous filaments, and agitates them to cause adjacent filaments to contact each other, to be entwined and gathered, thereby enabling the formation of a superficial layer of the three-dimensional structure  3.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resin-molded article with a springstructure, and to a method and apparatus for preparing a superficiallayer of such a resin-molded article with a spring structure. Morespecifically, the present invention aims to provide a resin-moldedarticle with a spring structure which comprises the loops and curls of athree-dimensional structure such as filaments of a resin extending in athree-dimensional space, and a method for improving the quality of asuperficial layer of the resin-molded article, thereby making theresin-molded article with a spring structure more adaptable to widelydifferent applications, and adding to the value of the resin-moldedarticle with a spring structure.

2. Description of the Prior Art

Various proposals as to the method of producing resin-molded articleswith a spring structure and apparatuses suitable for the manufacturethereof have been presented.

Such proposals can be seen, for example, in Japanese Unexamined PatentApplication Publications Nos. 1-207462, 1-241264, 5-106153, 7-68061,7-68284, 7-189106, 8-74161, 8-99093, and 9-21054, Japanese ExaminedPatent Application Publications Nos. 3-17668 and 4-33906, and WO01/68967A1.

Among such proposals, one advocates the use of an extrusion moldingsystem which is equipped with shoots for guiding filaments falling froma die.

An exemplary molding system comprises two rod-like heaters arranged onthe two long sides of a bundle of falling filaments (the bundle isresponsible for the formation of a three-dimensional structure asdescribed herein), and a pair of panels arranged beneath the respectiveheaters. Each panel consists of two strips: the upper strip forms aslope of about 45-80° with respect to a horizontal plane and the lowerone is submerged under cooling water. The two lower strips can be drivencentrally to enclose the bundle of filaments in a gap between them.

Another exemplary molding system comprises static or movable curvedplates coated with a fluorine resin arranged along a bundle of filamentsto modify the bundle into a three-dimensional structure whose densityand shape can be adjusted as desired.

See Japanese Examined Patent Application Publication No. 4-33906 and orWO 01/68967A1.

The applicants of the present invention had developed a system (to bereferred to simply as the pilot system hereinafter) for forming athree-dimensional structure as shown in FIGS. 12-15 during their pursuitof the present invention. The pilot system allows cooling water M toflow down over shoots 51 with which a bundle of melted continuousfilaments are firstly brought into contact so as to cool the bundle offilaments 2, to thereby prevent the adhesion of filaments to the shoots51. Each shoot 51 consists of a stainless steel plate whose workingsurface is coated with a fluorine resin. Coating of a fluorine resin isfor preventing the adhesion of filaments 2 to the shoot 51, andpromoting the spread of cooling water M over the shoot 51. Above eachshoot 51 consisting of a fluorine resin-coated plate, is placed a watertank 53 for storing cooling water which has, on its bottom, a row ofholes having a specified diameter being separated from each other with aspecified distance. The water tanks 53 shed, like a shower, a row ofcooling water M over the shoots 51. Melted filaments 2, being broughtinto contact with cooling water M flowing down over the shoots 51, aredistorted as a result of cooling and agitation, and the filaments nowdeformed in loops and curls fall into a water bath 26 below.

According to a system disclosed in the Japanese Examined PatentApplication Publication No. 4-33906, a bundle of filaments, when itreaches a level just above the surface of cooling water, is sandwichedby a pair of inclined upper strips which restrict the thckness of thebundle. Therefore, it may happen that parts of outward filaments falldirectly on the upper strips, slip thereon and plunge into the coolingwater.

A conventional system as disclosed in WO 01/68967A1 often producesresin-molded articles with a spring structure whose surfaces becomerough or nappy because of defective loop or curls formation.

The pilot system also exhibits following problems, and is restricted inits improvement of the quality of products.

The cooling water does not evenly spread over the shoots 51 because ofthe water-repellent activity of the fluorine resin coats. Thewater-repellent coat hinders the uniform spread of cooling water (seeFIGS. 12 and 15). Some thin water currents M independently flow downstraight over the shoots 51 after they contact with the latter, whileother thin water currents merge with each other. This makes it difficultto uniformly cool the entire lengthwise surfaces of a resin-moldedarticle with a spring structure. Moreover, filaments 2 slip so readilyon the fluorine resin-coated surfaces that the loop or curl formation ofthe filaments is disturbed (see FIG. 16(B)).

The joining distances (γ in FIG. 16(A)) required for gathering andcompressing continuous melted filaments are rather short. Even if thejoining distance is made large, the produced resin-molded article willhave an insufficient cushion property because of the fact that the threedimensional structure is not uniformly cooled with this system.

As a consequence, the resin-molded articles with a spring structureproduced by the pilot system exhibit following shortcomings.

Filaments are often cooled so much that the spring structural resinmolded product produced by the system have undulated surfaces (see FIG.15(A)). For example, on some parts of the shoots 51, water currentsmerge (see streak E of FIG. 14), and filaments exposed to such mergedcurrents are cooled so much that the resin constituting the filamentsshrinks and becomes less adhesive.

On the other hand, with regard to filaments exposed to independent thincurrents, they are not cooled so much that their loops and curls aredistorted. Thus, the filaments constituting the superficial layers 4, 5of a resin-molded article 3 with a spring structure produced by thepilot system often have defective loops and curls. When thin watercurrents merge into one, there is formed a water deficient line(s) (seestreak S of FIG. 14) on one or both sides of the thickened current.Melted continuous filaments exposed to such water deficient lines arenot sufficiently cooled, and mechanically so fragile that, when they arepulled downward during falling, they are easily cleaved. Their cut endsspread and exhibit a characteristic pattern. When the cut ends arespiky, they take pattern (1) (see FIG. 15(B)). When the cut ends arethread-like or cord-like and stretched during falling, they take pattern(2) (see FIG. 15(C)).

Thus, the water films formed over the shoots do not have a uniformthickness, and with regard to a resin-molded article with a springstructure exposed to such water films, fusion of adjacent loops andcurls is readily released (see FIG. 16(C)). This is because loops andcurls have different adhesive activities owing to the unevendistribution of cooling water on the shoots. When a three-dimensionalstructure affected with such defects is bent, fused portions of loopsand curls are easily separated giving a crush sound (see FIG. 16(C)).Such a three-dimensional structure may be defective in cushioningactivity and strength.

The defective formation of loops and curls is accompanied by thedistorted formation of individual filaments, resulted in changing insectional view of the filament. If the filament is a hollow filament,for example, it will have a distorted cross-section instead of a normalround shape.

Because with the pilot system it is not possible to exert strongcompression, the resin-molded article produced by the system cannot helpbut having a large thickness. If strong compression is simply appliedusing the pilot system without introducing any appropriate compensatorymodifications, the resulting resin-molded article will have a reducedcushion property as well as a reduced thickness.

When the pilot system exhibiting the shortcomings as described above isused for the production of resin-molded articles with a springstructure, the resin-molded articles or products using the resin-moldedarticle as a material exhibit following problems.

If it is required to insert a resin-molded article with a springstructure in a covering member, the undulated, nappy, or spiky surfacesof the article will get caught by the covering member, and damage thelatter, or conversely fused loops forming the surfaces of the articlewill be pulled apart to be damaged.

Fused joints of adjacent filaments of a three-dimensional structure aresusceptible to cleavage, and the cushioning property of a resin-moldedarticle deteriorates after long use.

The resin-molded article must have a comparatively large thickness whichleads to the enlargement of the volume. This causes clumsiness forhandling which may lead to the increase of a production cost.

In view of above, the present invention aims to provide a system forproducing a resin-molded article with a spring structure capable ofuniformly distributing cooling water over the entire surfaces of shoots,thereby relieving a three-dimensional structure of the risk of beingexposed either to thickened water currents or to thinned water currents,applying strong compression on the three-dimensional structure, andpreventing the separation of fused loops constituting thethree-dimensional structure. The present invention also aims to providea resin-molded article with a spring structure where the surfaces arepractically free from undulations, fusion of adjacent loops is preventedagainst separation, the cushioning property and strength are maintainedeven after long use, and its weight is comparatively light which isadvantageous from an economical viewpoint for the material.

SUMMARY OF THE INVENTION

The resin-molded article with a spring structure of the presentinvention is a three-dimensional structure including voids at apredetermined bulk density obtained by contacting, entwining, andgathering adjacent ones of random loops or curls of continuous, solidand/or hollow filaments made from a thermoplastic resin and/or athermoplastic elastomer. With regard to the resin-molded article with aspring structure, the bulk density of its oppositely disposedsuperficial layers may be 0.2 to 0.5 g/cm³, preferably 0.3 to 0.4 g/cm³.Their void ratio may be 44 to 77%, more preferably 56 to 67%. A corelayer sandwiched between the superficial layers may have a bulk densityof 0.01 to 0.15 g/cm³, preferably 0.03 to 0.05 g/cm³. Its void ratio maybe 83 to 99%, more preferably 94 to 97%.

The method of this invention for preparing the superficial layers of aresin-molded article with a spring structure comprises the steps offorming, during the production of a three-dimensional structureincluding voids at a predetermined bulk density which is obtained bycontacting, entwining, and gathering adjacent ones of random loops orcurls of continuous, solid and/or hollow filaments made from athermoplastic resin or a thermoplastic elastomer, exposing thelengthwise aspects of a three-dimensional structure comprising meltedfilaments extruded from a die to uniform cooling water films, andcausing peripheral filaments located along the lengthwise sides tocontact and fuse with each other to form loops and curls, and producinga three-dimensional structure whose oppositely disposed superficiallayers largely comprise loops and curls and have a higher density whilethe core layer sandwiched between the two superficial layers has a lowerdensity.

The system of the invention for preparing the superficial layer of aresin-molded article with a spring structure is a system for extruding amelt of a thermoplastic resin and/or thermoplastic elastomer to convertit into solid and/or hollow continuous filaments, causing adjacentfilaments to contact each other, entwine, and gather to form loops andcurls, and thus forming a three-dimensional structure having apredetermined bulk density.

The system of the invention is characterized by comprising a pair ofshoots whose opposite surfaces are inclined downward centrally suchthat, when a bundle of filaments are passed through a gap between theshoots, the filaments are gathered towards the center and compressedduring passage through the gap, water-permeating sheets covering the topsurfaces of the shoots, and cooling water supply portions which flowcooling water to produce currents in a space between thewater-permeating sheets and the top surfaces of the shoots, wherein somepart of the current penetrates the water-permeating sheet to form anoverlying current which uniformly spreads over the entire top surface ofthe water-permeating sheet, peripherally located continuous filamentsconstituting the lengthwise lateral portions of a three-dimensionalstructure are exposed to the uniform flow ends of water currents, to beagitated by the resulting eddies so much that they are deformed intoloops and curls, and adjacent loops and curls are fused with each otherthrough contact.

The “water-permeating sheet” is preferably made of a material such ascloth (bleached cloth) which allows water to permeate, is soft, and hasa higher frictional coefficient than does stainless steel or a fluorineresin. The water-permeating sheet moderates the impact exerted by watercurrents on filaments, and inhibits the smooth sliding of filaments viafrictions imposed on the filaments, thereby facilitating the filamentsto form loops and curls. The thickness of the water-permeating sheet maybe 0.001 to 1.0 mm, preferably 0.2 to 0.5 mm, or more preferably 0.3 to0.4 mm.

The “continuous filaments” may include filaments made from generalpurpose plastics (polyolefins, polystyrene resins, methacryl resins,poly vinyl chloride, etc.) or engineering plastics (polyamide,polycarbonate, saturated polyester, polyacetal, etc.). For example, theyare preferably made from thermoplastic elastomers such as polyethylene(PE hereinafter), polypropylene (PP hereinafter), PVC, or nylon. If thefilaments are hollow, the cavity within each filament may be continuous,or comprise a series of discrete cavities. For example, the cavity in afilament may be separated into sections with a septum placed betweenadjacent sections.

The advantages of the present invention are enumerated below.

Cooling water penetrating the water-permeating sheet appears on the topsurface of the sheet and forms an overlying current there and preventsthe adhesion of filaments to the shoot.

Since the water-permeating sheet has a higher frictional coefficientthan does a fluorine coated (Teflon™ or the like) surface or a stainlesssteel, it exhibits a higher resistance to the falling movement of meltedcontinuous filaments which helps the filaments to be deformed into loopsand curls.

Since a bundle of melted continuous filaments fall on thewater-permeating sheet covered with a water film which has a highcushioning activity, the filaments are protected against deformation.Particularly, if the filaments are hollow, it is possible to obtain aresin-molded article with a spring structure in which constituentfilaments have a cross-section practically free from distortions, whichadvantageously adds to the value of the resin-molded article.

The advantages provided by the method of this invention are as follows.

The method makes it possible to produce a resin-molded article with aspring structure whose surfaces are uniformly smooth.

Since the joining distances required for gathering and compressingmelted continuous filaments are comparatively large, wider portions oflengthwise arranged peripheral filaments are gathered and the resultingthree-dimensional structure is more strongly compressed. As aconsequence, fusion of adjacent filaments is more stressed, and thestructure has an enhanced strength and higher cushioning activity.

Use of the resin-molded article with a spring structure of the inventionas a material can provide following advantageous products.

It is possible to provide products which have a dense texture, arepractically devoid of free cut ends, and have smooth surfaces free fromundulations.

It is possible to provide products in which fusion of adjacent filamentsis firm.

It is possible to provide products which are excellent in pressuredispersion because the superficial layers are highly dense and theconstitutive filaments thereof are firmly fused to each other.

The product can have a small thickness, excellent cushion property, andresistance to collapse. It ensures a reduced cost and is resistant torepeated bending.

Loops and curls in the superficial layers of a product are generally inparallel with a direction in which the extruded filaments werepropelled, and they provide the product with an effective pressuredispersing activity. Loops and curls in the core layer are practicallyin parallel with the crosswise direction, and are responsible for thecushion property of the product.

BRIEF DESCRIPTION OF THE DRAWINGS

The object and advantages of the invention will become understood fromthe following detailed description of preferred embodiments thereof inconnection with the accompanying drawings in which like numeralsdesignate like elements, and in which;

FIG. 1 shows a resin-molded article 1 with a spring structure;

FIG. 2(A) shows the sectional view of a comparable resin-molded articlewith a spring structure, and FIGS. 2(B) and 2(C) the sectional views ofa resin-molded article with a spring structure embodying the invention;

FIG. 3 shows an exemplary method for producing a resin-molded article 1with a spring structure;

FIG. 4 shows another exemplary method for producing a resin-moldedarticle 1 with a spring structure;

FIG. 5 shows yet another exemplary method for producing a resin-moldedarticle 1 with a spring structure;

FIG. 6(A) shows the lateral view of a part of a three-dimensionalstructure, and FIG. 6(B) frontal view of the three-dimensionalstructure;

FIG. 7(A) shows the sectional view of a superficial layer-forming unit,and FIG. 7(B) the frontal view of the same unit with a water-permeatingunit being removed;

FIG. 8(A) shows the perspective view of the superficial layer-formingunit, and FIG. 8(B) the enlarged view of the same unit;

FIG. 9 illustrates the operation of the superficial layer-forming unit;

FIG. 10 schematically shows parts of different exemplary schemes forproducing a resin-molded article 1 with a spring structure;

FIG. 11 schematically shows how a three dimensional structure isprocessed by the method of the invention;

FIG. 12 shows the perspective view of a system previously developed bythe present applicants;

FIG. 13 shows the sectional view of a superficial layer-forming unit ofthe pilot system;

FIG. 14 shows the operation of the superficial layer-forming unitattached to the pilot system;

FIG. 15(A) shows undulations formed on the surface of a product producedby the superficial layer-forming unit of the pilot system. FIG. 15(B)shows pattern {circle around (1)} of disintegrated cut ends offilaments. FIG. 15(C) shows pattern {circle around (2)} of disintegratedcut ends of filaments, and

FIG. 16(A) compares the joining distance (δ) of the molding system ofthe invention with the joining distance (γ) of the pilot system. FIG.16(B) shows how a superficial layer of a three-dimensional structure isformed by the pilot system. FIG. 16(C) shows how the joints of fusedfilaments constituting a three-dimensional structure are separatedduring processing by the pilot system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Description of aSpring Structural Resin Molded Product 1

A resin-molded article 1 with a spring structure embodying the presentinvention is a three-dimensional structure 3 with voids obtained bycontacting, entwining, and gathering random continuous filaments 2(hereinafter also simply called “filaments” 2) made from or primarilyfrom a thermoplastic resin. The filaments 2 take the form of loops, andadjacent loops of the filaments contact, entwine and gather with eachother. The process necessary for the production of a resin-moldedarticle 1 with a spring structure is described later.

The dimensions of the resin-molded article 1 with a spring structure areas follows.

The bulk density of the resin-molded article 1 with a spring structureis 0.001 to 0.20 g/cm³.

The preferred range of the bulk density of resin-molded article 1 with aspring structure is as follows. The bulk density of the resin-moldedarticle 1 with a spring structure may be 0.08 to 0.20 g/cm³, preferably0.10 to 0.18 g/cm³. The void ratio of the resin-molded article 1 with aspring structure may be 78 to 91%, preferably 80 to 88%. Theresin-molded article 1 with a spring structure comprises front and rearsuperficial layers 4 and 5 with a core layer 6 in between. The bulkdensity of each superficial layer may be 0.2 to 0.5 g/cm³, preferably0.3 to 0.4 g/cm³. Its void ratio may be 44 to 77%, preferably 56 to 67%.The bulk density of the core layer may be 0.01 to 0.15 g/cm³, preferably0.03 to 0.05 g/cm³. The void ratio of the core layer may be 83 to 99%,preferably 94 to 97%.

The diameter of the filaments constituting the resin-molded article 1with a spring structure may be 0.3 to 3.0 mm, preferably 0.7 to 1.0 mmwhen the filaments are solid filaments. If the solid filaments had adiameter equal to or smaller than 0.3 mm, the filaments would loseresiliency and fusion of adjacent filaments occurs so frequently thatthe porosity of the resin-molded article would become undesirably low.On the contrary, if the solid filaments have a diameter equal to orlarger than 3.0 mm, the filaments would become so resilient that theywould not form loops, nor fuse with each other which would lead to thelowered strength. The diameter of the filaments constituting theresin-molded article 1 with a spring structure may be 1.0 to 3.0 mm,preferably 1.5 to 2.0 mm, most preferably 0.9 to 1.3 mm, when thefilaments are hollow. The void ratio of each hollow fiber is preferably10 to 80%. If the void ratio were equal to or lower than 10%, the hollowfilaments would lose the merit of reducing the weight of the productrelative to its bulk. On the contrary, if the void ratio were equal toor higher than 80%, the hollow filaments would have a reduced cushioningactivity.

The resin-molded article 1 with a spring structure may have a thicknessof 10 to 50 mm, preferably 20 to 40 mm. Its length and width may bedetermined as appropriate.

The resin-molded article 1 with a spring structure may have a void ratioin the range described below, to maintain its elasticity and strength aslong as it exists as a three dimensional structure, as well as to reduceits weight.Void ratio (%)=(1−bulk density/density of resin)×100

If a mixture of solid filaments and hollow filaments is used as amaterial of the filaments constituting a resin-molded article 1, themixing ratio of solid filaments to hollow filaments is preferably 0 to50:50 to 100.

Furthermore, if hollow filaments are placed at the core, and surroundedby solid ones which are placed in superficial layers, the resultingresin-molded article will be desirable because it will give an agreeabletouch feel.

The thermoplastic resin serving as a material of the resin-moldedarticle 1 with a spring structure includes particularly preferablypolyolefin resins such as polyethylene (PE), polypropylene (PP), etc. Avinyl acetate resin (VAC hereinafter), ethylene vinyl acetate copolymer(EVA hereinafter), or styrene butadiene styrene (SBS hereinafter) ispreferably used, or a mixture of them may be used. The polyolefin resinmay include recycled resins.

The thermoplastic resin is preferably made from a mixture obtained bycombining two or more chosen from polyolefin resins, vinyl acetateresins, ethylene vinyl acetate copolymers and styrene butadiene styrene.The resin-molded article 1 with a spring structure preferably comprisesa three-dimensional structure made from a mixture (e.g., thermoplasticelastomer) obtained by mixing a polyolefin resin such as PE or PP withVAC, EVA or SBS.

The mixing ratio of a poly olefin resin to VAC or EVA in terms of theweight of vinyl acetate of the latter may be 70 to 97 wt %:3 to 30 wt %,preferably 80 to 90 wt %: 10 to 20 wt %.

If the VAC or EVA content were equal to or lower than 3 wt %, the impactresilience of the three-dimensional structure would be reduced. On thecontrary, if the VAC or EVA content were equal to or higher than 30 wt%, the thermal stability of the three-dimensional structure would beimpaired.

The mixing ratio of a polyolefin resin to SBS may be 50 to 97 wt %:3 to50 wt %, preferably 70 to 90 wt %: 10 to 30 wt %.

System for Molding a Three-Dimensional Structure 10

An exemplary system 10 for molding a three-dimensional structurerepresenting an embodiment of the system for molding a resin-moldedarticle 1 with a spring structure mentioned above is described below. Asshown in FIGS. 3 and 4, the system, i.e., an extrusion molding system 20comprises a hopper 21. A thermoplastic resin is fed to the system viathe hopper 21, melted after being heating to a predeterminedtemperature, kneaded and transferred into a molding die 22. The melt isextruded at a predetermined speed through a plurality of nozzles 23, andfilaments to constitute a three-dimensional structure 3 are taken off bya winder 24.

Take-off rolls 25, 25 constituting the winder 24 are submerged underwater in a bath 26. Each of the take-off rolls 25, 25 comprises a pairof upper and lower rollers connected with an endless belt 28. A waterbath 26 has a water inlet valve 26 a and a water outlet valve 26 b. Aresin-molded article 1 with a spring structure is prepared from athree-dimensional structure 3 via the system: filaments 2 constituting athree-dimensional structure are deformed into random loops; adjacentrandom loops are brought into contact each other to be fused; and therandom loops as fused together become solidified after being cooled inwater. The take-up rolls 29, 29 lift the thus produced resin-moldedarticle 1 with a spring structure.

As seen from FIG. 4, if it is suspected that filaments constituting aresin-molded article 1 with a spring structure comprising athree-dimensional structure are undesirably resistive to bending whenthey are taken off by the take-off rolls 25, 25, it is possible todeliberately prepare low-density portions which are more sensitive tobending across the three-dimensional structure at regular intervals.Then, it is possible to bend the resin-molded article 1 at thoselow-density portions, after they are lifted from water. A cutting unit30 is used to cut the resin-molded article 1 with a spring structurelifted from the water into pieces having desired lengths.

FIG. 5 shows another exemplary system. This system further comprises acutting unit 130 placed in a water bath 126. The cutting unit 130 is putbelow and close to a winder 124. On a wall of the water bath 126opposite to the one to which the winder 124 is attached rests aconveying unit 135. The conveying unit 135 comprises a conveyor havingmultiple stopper spikes protruding from its surface. The stopper spikesare inserted into thin gaps between adjacent three-dimensional structurepieces obtained by cutting a three-dimensional structure sheet by meansof the cutting unit 130. The elements corresponding with those of theforegoing embodiment are represented by similar numerals with, however,1 being attached to the third place of the numerals.

Now, description is given on a superficial layer-forming unit 50. Thesuperficial layer-forming unit 50 is for increasing the density ofsuperficial layers of the resin molded article with a spring structure 1by operating on melted continuous filaments 2 extruded from a die 22,that is, by restricting/compressing the thickness of the filamentsbefore the filaments contact with water in a water bath 26, to producethereby a resin-molded article 1 with a spring structure having densesuperficial layers. Furthermore, according to the superficiallayer-forming unit 50, it is possible to ensure the smooth formation ofloops, and the uniform fusion of adjacent loops. Still further,according to the superficial layer-forming unit 50, it is possible tosolidify filaments before they contact with the surface of an endlessconveyor belt 28, thereby preventing the surface undulation of the beltfrom being printed on the filaments. Of course, this effect is moreapparent if the endless belt 28 is wound around a caterpillar (see FIG.12).

As shown in FIGS. 7-9, the superficial layer-forming unit 50 comprises apair of shoots 51 which are horizontally arranged along the twolengthwise sides of a three-dimensional structure 3 comprising multiplemelt filaments 2 which are extruded via a die 22 located upward to falldownward, the shoots 51 having symmetrical downward slopes in profile torestrict/compress the thickness of the three-dimensional structure 3passing through the gap between them so that the thickness of thethree-dimensional structure 3 is reduced at a specified ratio afterhaving passed through the gap, a pair of water supply portions 53located upward which supply water for cooling the three-dimensionalstructure 3, and a pair of water-permeating sheets 55 which cover thesurfaces of the shoots 51 and are attached to the water supply portions53.

Each shoot 51 comprises a bluntly inclined plate 51 a having a bluntlyinclined slope and a sharply inclined plate 51 b having a sharplyinclined slope which extends from the lower end of the bluntly inclinedplate 51 a. The lower ends of the sharply inclined plates 51 bpreferably correspond in profile with the inner edges of an endless belt28.

Generally, the shoot 51 is made from a metal, preferably stainlesssteel. This is because stainless steel is resistant to rusting even whenit is exposed to water. To be given excellent water repellent andspreading activity, the top surface of the shoot 51 is preferably coatedwith a fluorine resin.

In this particular system, a die outlet with nozzles 23 has arectangular cross-section with a length of 1300 mm and width of 80 mm.Each shoot 51 has a length of 1300 mm and thickness of 3 mm. The gapbetween oppositely disposed sharply inclined plates 51 b is set to be 40mm.

Beneath the shoots 51 is placed a winder 24 as described above. Thethickness of a resin-molded article 1 with a spring structure is reducedby 30 to 70% (compression ratio), preferably 40 to 60% with respect tothe thickness of a three-dimensional structure 3. In the particularexample shown in FIG. 6, a three-dimensional structure 3 has a width of80 mm, while a resin-molded article 1 with a spring structure preparedfrom the structure 3 has a thickness of 40 mm. The compression ratio isset to 50% in this case as is usually observed in the production ofresin-molded articles 1 with a spring structure.

Water-permeating sheets 55 similar to those of the foregoing embodimentare arranged in this system. They are preferably made of cloth (bleachedcloth), but may be made of a cloth substitute. The water-permeatingsheet 55 preferably allows water to pass through it to appear on itssurface. Then, cooling water C not only flows beneath thewater-permeating sheet 55 but also penetrates the sheet to appear on itstop surface. The water-permeating sheets 55 are for ensuring the uniformspread of cooling water C over the entire top surfaces of the shoots 51.The water-permeating sheets 55, when contacting with falling meltedfilaments, encourage the loop formation of the filaments with the aid ofthe frictional forces generated as a result of contact. Thewater-permeating sheet 55 preferably has a thickness of 0.3 to 0.4 mm.

As shown in FIGS. 6 and 7, each water supply portion 53 comprises a tank53 a for storing water which has a cubic shape with a rectangularcross-section, and is fixed lengthwise horizontally on the upper end ofbluntly inclined plate 51 a, cooling water outlets 53 b formed on thelowermost surface of tank 53 a for ejecting cooling water, a metal bar53 c with a C-shaped cross-section for attaching the water-permeatingsheet 55 to the tank 53 a, and screws 53 d for fastening the metal bar53 c to the tank 53 a. The cooling water outlets 53 b are formed on thelowermost surface of the tank 53 a. The shape of the cooling wateroutlet 53 b is not limited to any specific one, but is preferablyslit-like when viewed from front. Alternatively, it may take a round, orsquare shape instead of a slit-like shape. The cooling water outlet mayexist as discrete dots or as a linear slit. The tank 53 a is connectedvia a hose and tap to a water source (not illustrated), for example,public water supply.

As shown in FIG. 9, when cooling water C is transferred to the tank 53a, cooling water C is ejected from the outlets 53 b and allowed to flowbetween the water-permeating sheet 55 and the bluntly inclined plate 51a, to form an underlying current L. Some part of cooling water C passesthrough the water-permeating sheet 55, and appears on its top surface toform an overlying current M there. The overlying currents M on bothsides contact with the lengthwise sides of a three-dimensional structure3 to form eddies there, thereby facilitating filaments to form loops andadjacent continuous filaments to contact each other.

The course of a given filament, after being extruded from a nozzle ofthe die 22, is not uniform but random. But, generally speaking,filaments which will constitute the core layer 6 of a three-dimensionalstructure 3 tend to take a spiral course in the propulsion direction,while filaments which will form the superficial layers 4, 5 tend to takea loop course in parallel with the surfaces of the three-dimensionalstructure.

Although the water-permeating sheet 55 is soft, it hardly moves eventhough it is exposed to the currents of cooling water, and remainsstabilized. The water-permeating sheet 55 is permeable to water, andthus water from the underlying current L penetrates the water-permeatingsheet 55 to appear on its top surface to form an additional currentthere. The water-permeating sheet 55 spreads the overlying current somuch that the overlying current M having a uniform thickness is allowedto flow over the entire surface of the water-permeating sheet 55.Namely, the water-permeating sheet 55 absorbs some part of underlyingwater current and spreads it laterally on its top surface. Thus, thewater-permeating sheet 55 prevents the formation of thin threadcurrents, and their merging, and allows the overlying water current M tohave a uniform thickness. Accordingly, the water-permeating sheets 55allow the superficial layers 4, 5 of a three-dimensional structure to becooled uniformly. Moreover, since the water-permeating sheet 55 has ahigher frictional coefficient than does a metal, it exhibits a higherresistance to the falling movement of melted continuous filamentsconstituting a three-dimensional structure which causes the filaments tobe deformed into loops and curls by forcibly retarding their downwardfall. The water-permeating sheet 55 promotes the formation of more firmloops than are observed with a similar fluorine resin-coated sheetbecause it exerts stronger frictions upon the filaments than does thelatter.

A three-dimensional structure 3 including compactly folded loops in itssuperficial layers 4, 5 with the long axis of the loops in parallel withthe lengthwise surfaces is placed with respect to the overlying watercurrents M such that the folded loops are placed in parallel with theflow ends of the overlying water currents M to be cooled by the latter.Moreover, both the superficial layers 4, 5 are compressed.

On the other hand, filaments which will constitute the core layer 6 formspiral loops. Then, the three-dimensional structure 3 is captured by awinder 24.

The advantages of the present embodiment will be enumerated below.

A) Some part of water penetrates the water-permeating sheet 55 to forman overlying current M thereupon. This prevents the adhesion offilaments to the shoot 51.

B) The water-permeating sheet 55 has a higher frictional coefficientthan does a fluorine resin-coated surface or a metal, and thus itexhibits a higher resistance to the falling movement of meltedcontinuous filaments, thereby facilitating the filaments to be deformedin firm loops.

C) Melted continuous filaments fall on the water-permeating sheet 55covered with the overlying water current M both of which have acushioning activity. Thus, the filaments are encouraged to form firmloops, and the cross-section of the filaments 2 is protected againstdeformation. Although the filaments fall at a considerably high speed,they are allowed to form firm loops on account of the cushion activitiesof the water-permeating sheet 55 and overlying water current M withoutbeing distorted in their cross-section. The latter feature isparticularly advantageous if the filaments are hollow.

The advantages ensured by the method of the present invention are asfollows.

Loop separations are few. The moment fused filaments separate, theoverall strength of a three-dimensional structure greatly lowers. Tomaintain the strength of a three-dimensional structure, it is mostimportant to prevent the separation of fused filaments.

According to the pilot system, filaments slip so well that their loopformation is disturbed. According to the present system, there areformed two water currents one flowing over the water-permeating sheet 55and the other beneath the same. Therefore, even if filaments fall uponthe overlying currents to form loop there, the loop formation occurssmoothly because the overlying water current has a good cushionproperty, and the water-permeating sheet 55 exhibits such a strongfriction to the downward fall of the filaments as to retard the movementof the filaments.

It is possible to greatly restrict/compress the thickness of a bundle ofmelted continuous filaments extruded from the die. Because a bundle offilaments can be compressed in thickness so greatly that theentanglement of individual fibers is emphasized, and contact areasbetween adjacent loops are increased to facilitate their fusion.

It is possible to mold filaments into a resin-molded article with aspring structure whose surfaces are smooth.

Accordingly with the present system it is possible to provide productshaving following features.

Resin-molded articles produced with the system have smooth densesurfaces practically free from nap and undulations. Thus, even if theyare wrapped with a cover, they do not damage the cover.

Fusion of filaments in the superficial layers 4, 5 is so strong that itis refractory to separation.

Filaments in the superficial layers 4, 5 are so dense and their fusionis so strong that the resin-molded article is excellent in pressuredispersion. If the article is used as a material of cushion, andreceives the weight of a sitting person, the superficial layers of thecushion disperse the weight of the person, and prevents the core layer 6from being exposed to overweight. Therefore, even if the core layer hasa coarse texture, it can withstand a considerable weight, and thecushion keeps a sufficient buffering activity. In addition, thesuperficial layers 4, 5 are so dense that fused filaments in the layersare hardly pulled apart even if they are exposed to hard externalforces.

Fusion of adjacent loops is so strong that the layer comprising suchloops has a high bending resistance.

The three-dimensional structure 3 can be narrowed/compressed greatly inits thickness. Therefore, it is possible to produce a thin resin-moldedarticle with a spring structure. The loop formation in the superficiallayers 4, 5 is improved so much that, even if the resin-molded articlehas a small thickness, it can have a good cushion activity andresistance to collapse. Since the product has a small thickness, itshandling becomes easy, which leads to a reduced production cost.

Filaments in the superficial layers 4, 5 form loops (peripheral loops)whose long axes are vertical to the adjacent surfaces. On the otherhand, filaments in the core layer 6 form loops (central loops) whoselong axes are in parallel with the long axis of the three-dimensionalstructure. The core layer is responsible for the cushion activity of thethree-dimensional structure.

Method for Producing a Resin-Molded Article with a Spring Structure 1

An exemplary method for producing a resin-molded article 1 with a springstructure as described above is described below.

As shown in the diagrams of FIG. 10, according to the method of thisembodiment for producing a resin-molded article 1 with a springstructure, preferably, a polyolefin resin such as PE, PP or the like andanother resin such as VAC, EVA or SBS are fed, in appropriate amounts,via a supplier such as a tumbler or weighing feeder, and the yield isdry-blended, mixed, or dissolved in a solvent, kneaded and fragmentedinto pellets. The pellets are transferred to a hopper 21 of acompression molding system 20.

To be more specific, starting resins, e.g., PP and SBS are mixed with atumbler (KR mixer, Kato Scientific Instruments Co.) at 40 rpm for 15minutes.

Next, as seen from FIG. 3, a mixture comprising the starting resins isapplied via a hopper 21 to a uni-axial (axis diameter being 65 mm)compression molding system 20 (see FIG. 4). The mixture is melted at apredetermined temperature (200° C. for Examples 1 to 6, and 260° C. forExamples 7 to 9), and the melt is kneaded and subjected tomelt-extrusion at a predetermined speed through a plurality of nozzleson the extrusion surface of a molding die 22, taken off by a winder 24which is described later, and formed into solid and/or hollow continuousfilaments having a predetermined diameter (e.g., 600 to 90,000 deniers,preferably 3,000 to 30,000 deniers, more preferably 6,000 to 10,000deniers). The filaments 2 in a melted state are passed through asuperficial layer-forming unit 50 as described above with reference toFIGS. 6-9 and FIG. 11, which causes adjacent filaments 2 to contact eachother to be entwined into random loops having a diameter of 1 to 10 mm,preferably 1 to 5 mm. The contacted and entwined portions of filamentsare at least partially fused and bonded to one another. The filaments 2may comprise solid filaments and hollow filaments at a predeterminedratio.

The thickness and bulk density of a three-dimensional structure or amass of random loops may be determined as appropriate by adjusting thegap between the take-off rolls 25, 25 of winder 24 in a bath 26. Thethree-dimensional structure (e.g., 10 to 200 mm in width and 2,000 mm inlength) obtained by processing filaments 2 into a mass of random curlsor loops, and hardening them in water, is passed through a pair oftake-up rolls 29, 29 to produce a resin-molded article 1 with a springstructure.

When filaments 2 which have been formed into loops in water are takenoff by the winder 24, the cushion property of the resultingthree-dimensional structure may be altered as appropriate by adjustingthe take-off speed of the winder 24. The three-dimensional structure,when it is required to have a comparatively high bulk density, shouldhave a bulk density of 0.03 to 0.08 g/cm³, preferably 0.04 to 0.07g/cm³, most preferably, 0.05 to 0.06 g/cm³.

In taking off the filaments, the take-off speed of the winder 24 isadjusted to a low take-off speed at intervals of e.g., 3 to 5 m by e.g.,reducing the take-off speed of take-off rolls 25, 25 to a lowpredetermined level at certain predetermined regular intervals insynchrony with a timer. Then, it is possible to obtain a resin-moldedarticle 1 with a spring structure comprising a series of alternatehigh-density portions and low-density portions repeating at regularintervals (e.g., 30 to 50 cm) in a longitudinal direction, thehigh-density portions being formed when filaments are taken off at a lowtake-off speed while the low-density portions being formed whenfilaments are taken off at a high take-off speed.

As seen from FIG. 4, if it is expected that filaments constituting aresin-molded article 1 with a spring structure comprising athree-dimensional structure will hardly be bent as needed when they aretaken off by the take-off rolls 25, 25 at a normal constant speed, it ispossible to adjust the take-off speed of the winder as above to producea three-dimensional structure comprising a series of high-densityportions and low-density portions, such that the three-dimensionalstructure can be bent at their low-density portions. The resin-moldedarticle 1 with a spring structure obtained via the above-describedprocess is cut with a cutting unit 30 into pieces having a desiredlength.

The above-described process produces, for example, a resin-moldedarticle with a spring structure 1 having a bulk density of 0.03 g/cm³and thickness of 50 mm. The three-dimensional structure may be preparedfrom filaments made of one, or two or more kinds of resins.

Exemplary Molding Systems

The extrusion system used was a uni-axial extrusion system with adiameter of 90 mm. The starting material was an ethylene vinyl acetatecopolymer. The processing conditions were as follows. The temperature ofthe resin was 250° C.; the molding pressure 0.1 Mpa; the rotation of thescrew 30 rpm; the extrusion force 135 kg/hr; and the take-off speed 32.3m/hr.

Exemplary Resins Example for the Production of Which Two Kinds of Resinswere Blended at a Different Ratio (1)

Two kinds of resins including PE+VAC, PE+EVA and PP+SBS are combined atdifferent ratios to produce different kinds of three-dimensionalstructures which is a precursor of resin-molded articles 1 with a springstructure.

Blending of the resins was achieved by using a tumbler (KR mixer, ModelKRT-100, Kato Scientific Instruments Co.) at 40 rpm for 15 minutes.Molding of the resin blend was achieved by using a uni-axial (axisdiameter being 65 mm) compression molding system: the screw was rotatedat 60 rpm; and take-off speed set at 3.1 or 0.6 m/min. The meltingtemperature of the resin blend was set to 200° C.

Example for the Production of Which Two Kinds of Resins Were Blended ata Different Ratio

Exemplary blends were prepared by combining PE 70 wt % or more +VAC30-90 wt %, PE 34-89 wt %+EVA 66-11 wt %, and PP 70-95 wt %+SBS 30-5 wt%. Those blends were extruded at 28 kg/h to produce resin-moldedarticles with a spring structure having a thickness of 50 mm and lengthof 300 mm. The physical dimensions of each product were as follows: thebulk density was 0.03 g/cm³; diameter of filaments 1.5 mm; surface area300×300 mm²; and thickness 50 mm.

Example for the Products Having Different Bulk Densities

A blend obtained by combining PE and VAC at PE:VAC=90:10 was used toprovide resin-molded articles with a spring structure which havedifferent bulk densities. Blending of the resins was achieved by using atumbler (KR mixer, Model KRT-100, Kato Scientific Instruments Co.) at 40rpm for 15 minutes. Molding of the resin blend was achieved by using auni-axial (axis diameter being 65 mm) compression molding system: thescrew was rotated at 60 rpm; and take-off speed set at 3.1 or 0.6 m/min.The melting temperature of the resin blend was set to 200° C.

A similar blend was obtained by combining 90 wt % of PE and 10 wt % ofVAC. The blend melt was extruded at 28 kg/h, and taken up at 3.1-0.6m/min.

The physical dimensions of each product were as follows: the bulkdensity was 0.01 and 0.05 g/cm³; diameter of filaments (hollow) 1.5 mm;surface area 300×300 mm²; and thickness 50 mm.

All the exemplary products exhibited no notable yielding points. If theproduct that does not exhibit a notable yielding point is used as a padof a cushion, the cushion will not show a deep dimple even when itreceives a heavy load, but disperse the load so uniformly over its topsurface that every part of the top surface will equally support theload.

If the product was bent by 50% or more, the resulting strain did notshow a sharp rise. If that three-dimensional structure was deformed inthe width direction by up to 90%, the deformation was reversible. If theproduct is used as a pad of a cushion, and a man sits on the cushion, hewill never feel like falling down to a hard bottom. The cushion, as soonas the load is relieved, will recovers its original form, and beresistant to collapse.

Next, the three-dimensional structure which serves as a precursor of allthe exemplary resin-molded articles 1 with a spring structure wascompared with a conventional three-dimensional structure prepared fromPP alone by a conventional method. One comparable sample had a notableyielding point, exhibited a sharp rise in strain when bent by a heavyload, underwent plastic deformation, and did not recover its originalform when extremely bent. Another comparable sample did not have ayielding point, exhibited a sharp rise in strain when bent by 50% ormore, and, when it was used as a pad of cushion, caused a person sittingon the cushion to feel like falling down to a hard bottom. Further, thissample underwent plastic deformation and did not recover its originalform when extremely bent.

It is possible according to this exemplary method of the invention toprovide a resin-molded article 1 with a spring structure having adesired hardness by adjusting the blending ratio of combined resins, andthe bulk density of a three-dimensional structure of the resin-moldedarticle 1.

The exemplary three-dimensional structure showed as high resistance tocollapse as did a similar, urethane foam-based structure.

The impact resilience of the exemplary three-dimensional structure wasas high as 91%. The exemplary product of the invention showed an impactresilience 1.4 time higher than did a comparable product made ofurethane foam.

The resin-molded article with a spring structure embodying the presentinvention is not limited to those described above, but may includevarious variants as long as the variants are included within thetechnical scope of the invention. It is also possible to modify thepresent invention without departing from the spirit of the invention. Itshould be understood that such variants, modifications and equivalentsare also included within the technical scope of the invention.

Thus, the broadest claims that follow are not directed to a machine thatis configure in a specific way. Instead, said broadest claims areintended to protect the heart or essence of this breakthrough invention.This invention is clearly new and useful. Moreover, it was not obviousto those of ordinary skill in the art at the time it was made, in viewof the prior art when considered as a whole.

Moreover, in view of the revolutionary nature of this invention, it isclearly a pioneering invention. As such, the claims that follow areentitled to very broad interpretation so as to protect the heart of thisinvention, as a matter of law.

It will thus be seen that the objects set forth above, and those madeapparent from the foregoing description, are efficiently attained andsince certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatters contained in the foregoing description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. It is also to be understood that the following claimsare intended to cover all of the generic and specific features of theinvention herein described, and all statements of the scope of theinvention which, as a matter of language, might be said to falltherebetween.

Now that the invention has been described;

REFERENCE NUMERALS

-   -   1: Resin-molded article with a spring structure    -   2: Filament    -   3: Three-dimensional structure    -   4, 5: Superficial layers    -   6: Core layer    -   10: System for molding a three-dimensional structure    -   20: Extrusion molding unit    -   21: Hopper    -   22: Molding die    -   23: Nozzle    -   24: Winder    -   25, 25: Take-off rolls    -   26, 126: Bath    -   27: Roller    -   28: Endless belt    -   29, 29: Take-up rolls    -   30, 130: Cutting unit    -   50: Superficial layer-forming unit    -   51: Shoot    -   53: Water supply portion    -   55: Water-permeating sheet    -   51 a: Bluntly inclined plate    -   51 b: Sharply inclined plate    -   C: Cooling water    -   53 a: Tank    -   53 b: Cooling water outlet    -   53 c: Holding metal bar    -   53 d: Screw    -   L: Overlying water current    -   M: Underlying water current

1. A resin-molded article with a spring structure comprising athree-dimensional structure including voids at a predetermined bulkdensity, the three-dimensional structure being obtained by contacting,entwining, and gathering adjacent ones of random loops or curls ofcontinuous, solid and/or hollow filaments made from a thermoplasticresin and/or a thermoplastic elastomer in such a manner as to allow theresulting structure to have a layered structure in which oppositelylengthwise disposed superficial layers have a bulk density of 0.2 to 0.5g/cm³, and a core layer sandwiched by the superficial layers has a bulkdensity of 0.01 to 0.15 g/cm³.
 2. A resin-molded article with a springstructure as in claim 1 in which each superficial layer has a bulkdensity of 0.3 to 0.4 g/cm³, and void ratio of 44 to 77%, and the corelayer has a bulk density of 0.01 to 0.15 g/cm³ and void ratio of 83 to99%.
 3. A resin-molded article with a spring structure as in claim 2 inwhich each superficial layer has a void ratio of 56 to 67%, and the corelayer has a bulk density of 0.03 to 0.05 g/cm³ and void ratio of 94 to97%.
 4. A resin-molded article with a spring structure as in claim 1 inwhich a mixing ratio of solid filaments to hollow filaments ispreferably 0 to 50:50 to
 100. 5. A resin-molded article with a springstructure as in claim 1 in which said hollow filaments are placed at acore, and surrounded by solid ones which are placed in superficiallayers.
 6. A method for producing superficial layers of a resin-moldedarticle with a spring structure comprising a three-dimensional structureincluding voids at a predetermined bulk density, comprising, whenobtaining the three-dimensional structure by extruding a melt of athermoplastic resin and/or a thermoplastic elastomer into meltedcontinuous filaments, and causing adjacent filaments to contact eachother, entwine and gather to form random loops and curls, the steps of:exposing the opposite lengthwise surfaces of a three-dimensionalstructure comprising melted filaments extruded from a die to theuniformly flowing currents of cooling water such that the lengthwisesurfaces of the three-dimensional structure are agitated by the currentsat an extended distance, which cause adjacent continuous filaments tocontact each other, and entwine to form loops and curls; and producing athree-dimensional structure having a layered structure in whichsuperficial layers comprising loops and curls have a high bulk densityand a core layer sandwiched by the superficial layers has a low bulkdensity.
 7. A system for producing superficial layers of a resin-moldedarticle with a spring structure comprising a three-dimensional structureincluding voids at a predetermined bulk density, the three-dimensionalstructure being obtained by extruding a melt of a thermoplastic resinand/or a thermoplastic elastomer into melted continuous solid and/orhollow filaments, and causing adjacent filaments to contact each other,entwine and gather to form random loops and curls, comprising asuperficial layer-forming unit which includes: rectangular shoots eachhaving an inclined surface placed opposite to each other with a gap inbetween to receive the filaments in such a manner as to shift the gapbeing narrower in lengthwise of extruding the filaments passing throughthe gap; water-permeating sheets which cover the top surfaces of therespective shoots; and cooling water supply portions each of which flowswater between a water-permeating sheet and the top surface of a shoot,wherein some part of the water flow penetrates the water-permeatingsheet to appear on its top surface to form there an overlying watercurrent uniformly spreading lengthwise, while the other part of thewater flow forms an underlying water current, and peripheral filamentsconstituting a lengthwise surface of a three-dimensional structure whichwill constitute a superficial layer of the three-dimensional structureis exposed to and agitated by the flow end of an overlying current suchthat adjacent filaments are caused to contact each other, entwine andgather to form loops and curls.
 8. A system for producing superficiallayers of a resin-molded article with a spring structure as claim 7 inwhich the water-permeating sheet is made of a material such as clothwhich allows water to permeate, and has a higher frictional coefficientthan does stainless steel or a fluorine resin.
 9. A system for producingsuperficial layers of a resin-molded article with a spring structure asclaim 7 in which said each shoot consists of a stainless steel platewhose working surface is coated with a fluorine resin.